In a lecture titled "How To Spend $50 Billion to Make the World a Better Place", Lomborg argued that a prioritised "to-do" list was necessary in order to achieve the best possible results when tackling some of the most pressing global issues such as HIV/AIDS, starvation, global conflict and climate change.

Lomborg recounted that when he asked the same question to a group of economists, including four Nobel laureates, in Denmark in 2004 - dubbed The Copenhagen Consensus - the economists found that spending $US27 billion on an HIV/AIDS prevention program would be the best possible investment for humanity. More than 28 million lives would be saved within six years and the flow-on effects would include increased productivity.

Providing micronutrient-rich dietary supplements to the malnourished, trade liberalisation and controlling malaria were also found to have benefits that far outweighed the costs, he said. However, spending the world's limited resources combating climate change would cost more than it would achieve, he argued.

Lomborg told the Sydney Ideas audience that priorities needed to be debated and set by democracies, based on what initiatives have the greatest benefits rather than the "ones with the most vocal advocates".

Bjorn Lomborg is the organiser of the Copenhagen Consensus, an adjunct professor at the Copenhagen Business School, author of The Skeptical Environmentalist and editor of How to Spend $50 billion To Make The World A Better Place . He is in Australia as a guest of the Centre for Independent Studies."How to Spend $50 Billion to Make The World A Better Place" was part of the University of Sydney's international public lecture series, Sydney Ideas.